What the controls do
The Energy Saving Trust says a heat pump comes with a programmer and thermostat, plus many other options for controlling the heat pump itself. Your installer should set everything up after asking about your heating preferences. The programmer and thermostat do the same job as a boiler’s, but they probably look and feel different, so make sure the installer explains them. The Trust also says many controls exist so the system adjusts itself to changing conditions, so provided it has been set up correctly you should not need to keep altering it.
Weather compensation and the heating curve
This is the control with the most effect on running cost. The Trust says the system should vary the flow temperature with the season, hot enough to heat the home in cold weather but cooler in warm spells to run more efficiently, and calls this weather compensation. It is also known as the heating curve. The curve is a line linking outside temperature to the water temperature sent to the radiators; the Trust’s example graph runs from a very cold day on the left to milder days on the right.
Installers sometimes set the curve higher to guarantee comfort in the coldest weather. The Trust says you may be able to reduce it significantly without the house feeling too cold, and suggests trying lowering it in one-degree steps through winter until the home feels too cold, then putting it back up one degree. It also warns against changing the settings unless you know what you are doing, and says your installer should be happy to help if the system is not meeting your needs. If you are unsure, ask them to check the curve rather than experiment.
Flow temperature and efficiency
Flow temperature is the temperature of the water leaving the heat pump. Lower is more efficient. In the Energy Systems Catapult trial the median COP was 3.5 when producing 35°C water, 2.38 at 55°C and 2.02 above 65°C. Across the monitored air source units the mean operating flow temperature was 39.7°C, and of the 165 heat pumps that reached a 65°C flow temperature at any point, 139 spent less than 1% of the time above it, which the report suggests reflects weather compensation. The Trust gives a practical translation: radiators on a boiler typically run at 75°C, but with a heat pump they will run closer to 45°C, so if you carried on heating in the same on-off pattern they might not be big enough.
| Lever | Effect | Who adjusts it |
|---|---|---|
| Heating curve | Sets flow temperature for each outside temperature | Installer; you with care |
| Radiator size | Bigger radiators allow lower flow temperatures | Design stage |
| Room thermostat set-point | Target room temperature | You |
| Schedule / set-back | Avoids large daily swings | You |
| Hot water schedule | Shifts water heating to cheaper or milder periods | You or installer |
The Trust notes that upgrading single-panel radiators to double or triple panels adds surface area without extra wall space. That design link is covered in the sizing and radiators guide, and what flow temperature does to efficiency is in the efficiency guide.
Schedules, set-back and the thermostat
In the UK we are used to switching heating on in the morning, off for work and on again in the evening. The Trust says that is poor practice for a heat pump. It recommends keeping the heating running for extended periods and using a set-back, lowering the temperature by a few degrees when you are out or asleep, instead of switching off. Reheating a cooled house forces the heat pump to work much harder. It also says to avoid heating the house or water overnight on a standard tariff, when outside air is colder, unless you are on a time-of-use tariff with cheaper night rates.
For poorly insulated homes the Trust adds: keep the heating at a steady level, bring it on earlier in the morning, and do not worry if the radiators do not feel very hot, because they will still warm the room if left on long enough. Tariff choices interact with all of this; see the tariff guide for time-of-use options at the 1 October to 31 December 2026 cap.
Hot water and boost settings
The hot water cylinder has its own schedule and a periodic high-temperature cycle. The Trust says building regulations advise that cylinders regularly reach above 60°C to protect against Legionella, and that if bills are high it may be because that cycle runs too often. For most people it says weekly is safe, and you do not need it daily if you are home regularly. Set it for the cheapest period.
The “heating boost” or “comfort” setting adds an extra heater element in very cold spells. The Trust says it should not add much to bills over a year, but if you use it regularly, the radiators may be too small or the curve may be set wrongly, which is a conversation to have with the installer. If a fault message appears, do not ignore it; the service guide covers fault handling.
Getting it right at handover
Commissioning is when controls get set. The Trust says the installer should make sure you understand how the controls work, how to use them for a warm home and an efficient system, and give you warranty information, instructions and documents. Ask for the heating curve values to be written down so you can restore them. See the installation process for the whole handover, and the survey guide for what to settle before work starts.